Detective quantum efficiency of electron area detectors in electron microscopy.

McMullan G, Chen S, Henderson R, Faruqi AR - Ultramicroscopy (2009)

Bottom Line:
Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology.In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated.We also show that part of the response of the emulsion in film comes from light generated in the plastic support.

ABSTRACTRecent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology. We present MTF and DQE measurements for four types of detector: Kodak SO-163 film, TVIPS 224 charge coupled device (CCD) detector, the Medipix2 hybrid pixel detector, and an experimental direct electron monolithic active pixel sensor (MAPS) detector. Film and CCD performance was measured at 120 and 300 keV, while results are presented for the Medipix2 at 120 keV and for the MAPS detector at 300 keV. In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated. We also show that part of the response of the emulsion in film comes from light generated in the plastic support. Computer simulations of film and the MAPS detector have been carried out and show good agreement with experiment. The agreement enables us to conclude that the DQE of a backthinned direct electron MAPS detector is likely to be equal to, or better than, that of film at 300 keV.

fig2: Illustration of ESF and MTF calculations. (a) shows the calculated ESF (solid) from a simulated image of a perfect pixel detector and the corresponding fits based on models using a single Gaussian (dashed). The fit obtained using a single Gaussian with sinc correction is not shown as it is indistinguishable from the calculated ESF result. (b) shows the MTF results of a perfect detector MTF (solid) and that obtained from the single Gaussian fit (dashed). The MTF of the single Gaussian with sinc correction is indistinguishable from the perfect detector result. (c) shows the calculated ESF (grey) calculated from the measured 300 keV edge image of the MAPS detector and corresponding fit based on a double Gaussian model (dashed). (d) compares the calculated MTF obtained from the double Gaussian fit (dashed) and double Gaussian fit with sinc correction (solid). Also shown (but offset by vertically) is a comparison of the MTF from the double Gaussian fit (dashed) and that calculated via the numerical differentiation of the ESF (solid).

Mentions:
Calculation of the MTF based on a fit to ESF is illustrated in Fig. 2, which shows the results from a simulated edge image of a perfect pixel detector and the measured edge image at 300 keV recorded on the MAPS detector. The fit to simulated ESF as shown in Fig. 2a, is not improved by using more than a single Gaussian. The fit obtained using a single Gaussian with Eq. (15), is indistinguishable from the ESF and not shown. The calculated MTF is similarly indistinguishable from that of a perfect pixel detector.

fig2: Illustration of ESF and MTF calculations. (a) shows the calculated ESF (solid) from a simulated image of a perfect pixel detector and the corresponding fits based on models using a single Gaussian (dashed). The fit obtained using a single Gaussian with sinc correction is not shown as it is indistinguishable from the calculated ESF result. (b) shows the MTF results of a perfect detector MTF (solid) and that obtained from the single Gaussian fit (dashed). The MTF of the single Gaussian with sinc correction is indistinguishable from the perfect detector result. (c) shows the calculated ESF (grey) calculated from the measured 300 keV edge image of the MAPS detector and corresponding fit based on a double Gaussian model (dashed). (d) compares the calculated MTF obtained from the double Gaussian fit (dashed) and double Gaussian fit with sinc correction (solid). Also shown (but offset by vertically) is a comparison of the MTF from the double Gaussian fit (dashed) and that calculated via the numerical differentiation of the ESF (solid).

Mentions:
Calculation of the MTF based on a fit to ESF is illustrated in Fig. 2, which shows the results from a simulated edge image of a perfect pixel detector and the measured edge image at 300 keV recorded on the MAPS detector. The fit to simulated ESF as shown in Fig. 2a, is not improved by using more than a single Gaussian. The fit obtained using a single Gaussian with Eq. (15), is indistinguishable from the ESF and not shown. The calculated MTF is similarly indistinguishable from that of a perfect pixel detector.

Bottom Line:
Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology.In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated.We also show that part of the response of the emulsion in film comes from light generated in the plastic support.

ABSTRACTRecent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology. We present MTF and DQE measurements for four types of detector: Kodak SO-163 film, TVIPS 224 charge coupled device (CCD) detector, the Medipix2 hybrid pixel detector, and an experimental direct electron monolithic active pixel sensor (MAPS) detector. Film and CCD performance was measured at 120 and 300 keV, while results are presented for the Medipix2 at 120 keV and for the MAPS detector at 300 keV. In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated. We also show that part of the response of the emulsion in film comes from light generated in the plastic support. Computer simulations of film and the MAPS detector have been carried out and show good agreement with experiment. The agreement enables us to conclude that the DQE of a backthinned direct electron MAPS detector is likely to be equal to, or better than, that of film at 300 keV.